In designs of conventional, prior art check valves, the position of the clapper is generally not detectable without introducing a leak path in the valve body. The only position that can be detected is the locked open position, as this is usually detectable by means of an external device located on the operator located outside the valve body. The operator is the mechanical or hydraulic equipment used to actuate the valve. When the clapper in conventional check valves is in free swinging motion, however, the actual position of the clapper is not detectable.
Knowing the actual position of the clapper can be of crucial importance to ensure correct functioning of the check valve itself and the plant. The plant is the production system, which includes but is not limited to the pipeline assembly. Moreover, monitoring the position of the clapper can permit the anticipation and correction of potential failures associated with the valve, thereby preventing or reducing the adverse consequences of such failures on the entire plant.
The present, improved Continuous Magnetic Motion Position Indicator (CMMPI) comprises a magnetic joint assembly and a remote position transmitter and/or local visual indicator which can be in single or multiple forms. The magnetic joint transmits rotary movement of the clapper from the valve's clapper stem (inside the valve body) to the position indicator stem (outside the valve body), without the presence of dynamic seal interface(s).
The rotation of the valve stem is transferred to the remote rotary position transmitter, which converts the rotary movement of the clapper to a current signal for remote monitoring. A visual local position indicator can also be included in the design.
In the present, improved CMMPI, the magnetic joint comprises a set of magnets inside the valve body that interfaces with another set of magnets located outside the valve body. Proper orientation of the magnetic fields and the location of the magnets, as well as the selection of materials for the components involved, provide for reliable and durable operation of the joint assembly.
One type of magnet that can be employed in the present CMMPI is a permanent magnet. Orientation of the magnets is alternatively North-South-North-South. The external set is opposite in polarity to the internal set.
Components for the present CMMPI can be selected to be resistant to the process fluid and to sea water. In addition, material selection should account for the ferromagnetic properties of the materials employed to alleviate potential interference with the magnetic fields.
The present CMMPI system can be fitted with various types of remote rotary transmitters, and the number of transmitters can vary depending on the level of redundancy required or desired.